We are investigating the biotransformation of foreign organic compounds in hepatic and extrahepatic tissues of vertebrate and invertebrate marine species from coastal Maine and Florida. Both cytochrome P-450-dependent microsomal mixed-function oxidases and alkene- and arene oxide-metabolizing enzymes (epoxide hydrase and glutathione S-transferases) are being characterized in control fish and in fish pre-exposed to environmental contaminants such as polycyclic aromatic hydrocarbons or dioxins. BIBLIOGRAPHIC REFERENCES: Bend, J.R., Pohl, R.J., Arinc, E., and Philpot, R.M.: Hepatic microsomal and solubilized mixed-function oxidase systems from the little skate, Raja erinacea, a marine elasmobranch. Proc. Third International Symposium on Microsomes and Drug Oxidations, Berlin, Germany, July, 1976. In Conney, A.H., Estabrook, R.W., Hildebrandt, A.G., and Ullrich, V. (Eds.) Oxford, Pergamon Press. In press. Bend, J.R., Miller, D.S., Kinter, W.B., and Peakall, D.B.: DDE-Induced microsomal mixed-function oxidases in the puffin (Fratercula arctica). Biochem. Pharmacol. 26: 1000-1001, 1977.